Diagram of counting and centroiding with half-pixel precision. The lattice of squares denotes the pixel matrix of a counting camera, and the noisy background represents the readout noise. The small black dot denotes an incident primary electron which stimulates signals (green spot) around it. The peak position of the green spot is centroided with half-pixel precision, and then its intensity is digitalized and counted as one. Consequently, the point spread effect and readout noise are eliminated from the final output image.